(1) Field of the Invention
The present invention relates to an ATM (Asynchronous Transfer Mode) network communication route monitoring system, and more particularly to a communication route monitoring system for monitoring a communication route, using OAM (Operation And Maintenance) loopback cells, in an ATM network which is made up of virtual paths (VP) or virtual channels (VC) and a plurality of communication devices for terminating or relaying the virtual paths or virtual channels.
More specifically, the present invention is concerned with an apparatus for maintaining, operating, and monitoring an ATM network, and provides a capability for confirming a VP/VC route using a loopback function which is one of fault management functions of OAM cells, even if there is no unitary management function of network maintenance. The present invention also provides a capability for identifying a cell transfer fault location, and automatically detecting a malfunction of a communication route and displaying communication route information, by collecting communication route information such as traffic information, performance information, etc. on the communication route, even in the absence of a unitary management function of network maintenance.
(2) Description of the Related Art
ATM networks provide PVC (Permanent Virtual Connection) services including point-to-point services and point-to-multi-point services, and also provide VC (Virtual Connection) services, making available a wide variety of path forms to which subscribers can connect. There have been growing connections between different multi-vendor communication systems. For these reasons, problems imposed on network communications have been diversified. In view of those diverse problems, there has been a demand for a function of automatically inspecting or specifying problems on communications between subscribers.
Heretofore, Japanese laid-open patent publication No. 7-235929 has disclosed a method of generating and updating path route information using an OAM loopback cell function as one way of maintaining, operating, and monitoring an ATM network. According to the disclosed method, three OAM loopback cell types, i.e., an OAM loopback cell for indicating a start of test, an OAM loopback cell for indicating particular-position loopback, and an OAM loopback cell for indicating an end of test, are provided for an arrangement equipped with an operation system (OpS) for managing a network and various network elements (NE) of the network. These OAM loopback cells are transmitted from an NE at one end of a path to be inspected for its route to another NE at a terminal end of the path.
Each of the NEs which have received an OAM loopback cell for indicating a start of test relays the OAM loopback cell to a next NE, and turns on a flag. Then, the NE at the one end of the path transmits an OAM loopback cell for indicating particular-position loopback. This OAM loopback cell is delivered individually to those NEs which are positioned on the path, with the names of the NEs being indicated, among all the NEs whose data are stored in a database of the operation system. The NEs which have received the OAM loopback cell addressed thereto return the received OAM loopback cell together with information representative of the reception of the cell, and turn off the flag. The OAM loopback cell which has reached the NE at the terminal end without being returned by any NE is returned as one having no destination.
Finally, the NE at the one end of the path transmits an OAM loopback cell for indicating an end of test. When each of the NEs has received this OAM loopback cell, it relays the cell to a next NE. If the flag of its own remains on, each of the NEs indicates to the operation system that it has not received an OAM loopback cell for indicating particular-position loopback.
The operation system adds the NE which has indicated that it has not received an OAM loopback cell for indicating particular-position loopback, as an NE positioned on the path inspected for its route to the database, and deletes the NE addressed by the cell which has been returned from the NE at the terminal end as one having no destination, from the group of NEs positioned on the path in the database.
In this manner, a VP/VC route is confirmed using the OAM cell loopback function in the ATM network.
According to the conventional method, however, it is necessary for the network to have the operation system (OpS) which provides a centralized maintenance and management function. It has been impossible with the conventional method to confirm communication routes in those networks which are not equipped with the operation system (Ops).
Furthermore, the conventional method requires that an OAM loopback cell for indicating an end of test reach each of NEs. Therefore, the conventional method is not effective in the event of a circuit disconnection in the path being inspected. Specifically, the communication route up to the fault location cannot be confirmed while the communication route up to the fault location remains connected. Naturally, the fault location cannot be identified.
In those networks which are not equipped with the operation system, NEs that perform a network management function are required to recognize traffic information, performance monitoring information, and congestion information. These requirements, however, cannot be met by the conventional method.